1. Field of the Invention
This invention relates to a lawn mower with a vehicle body; an engine mounted on the vehicle body; caster-type front wheels; a rear wheel unit having a left rear drive wheel and a right rear drive wheel; a mower unit disposed between the front wheels and rear wheel unit; a left stepless transmission for transmitting drive, switched between forward drive and backward drive, to the left rear wheel; and a right stepless transmission for transmitting drive, switched between forward drive and backward drive, to the right rear wheel; wherein the right and left stepless transmissions are operable independently of each other.
2. Description of the Related Art
A lawn mower of this type has an advantage that the vehicle body turns with a small radius about a middle position between the right and left rear wheels when the rear wheels are driven to rotate at the same speed in opposite directions. However, as the center of gravity of the vehicle body is located relatively rearwardly, a lawn mower has been developed which has an auxiliary ground wheel fixed to the rear of the vehicle body for contacting the ground rearwardly of the rear wheels. This construction prevents lifting of the front of the vehicle body to avoid poor grass cutting results.
Such an auxiliary ground wheel fixed to the vehicle body could adversely affect the running performance of the lawn mower, depending on the position or support structure of the auxiliary ground wheel. For example, the auxiliary ground wheel impairs the turning performance of the vehicle and tends to produce body vibration during a run.
The object of this invention is to provide a lawn mower with an auxiliary ground wheel mounted in a manner not adversely affecting its running performance.
In order to achieve the above object, with a lawn mower set forth at the outset hereof, this invention provides a caster-type auxiliary ground wheel unit disposed rearwardly of the rear wheel unit and supported by a support member to be vertically movable relative to the vehicle body, and a braking mechanism for braking an upward movement of the support member.
With a rigidly fixed auxiliary ground wheel not vertically movable relative to the vehicle body, a strong reaction force acts on the auxiliary ground wheel when the vehicle goes up a sloping terrain. This reaction force from the ground constitutes a resistance to vehicle movement. In the worst case, the vehicle is unable to advance to the sloping terrain. According to this invention, the auxiliary ground wheel is movable up and down through the support member so that an upward movement of the auxiliary ground wheel prevents excessive reaction forces from generating when the vehicle travels on a sloping terrain. With a structure for allowing free vertical movements of the auxiliary ground wheel, the auxiliary ground wheel does not support the rear portion of the vehicle body for stable running, as a matter of course. The braking mechanism acts to produce a predetermined supporting force.
Preferably, this braking mechanism is provided in the form of a biasing mechanism, and more preferably in the form of a suspension spring, to bias the auxiliary ground wheel downward. When the vehicle travels on an uneven terrain, the auxiliary ground wheel is raised relative to the vehicle body by a reaction force from the ground, and at the same time lowered relative to the vehicle body by the suspension spring. Thus, the auxiliary ground wheel keeps contact with the ground while the vehicle travels over an uneven terrain. When the vehicle advances to an uphill terrain, the auxiliary ground wheel is raised relative to the vehicle body by a reaction force from the ground. As a result, the vehicle body is kept in contact with the ground by the auxiliary ground wheel, while preventing the generation of body vibration and changes in the body orientation caused by ups and downs of the auxiliary ground wheel. When the mower travels over an uneven terrain, and the auxiliary ground wheel is prevented from acting as a traveling resistance which would not allow the vehicle to advance to an uphill ground.
In a preferred embodiment of the invention, the auxiliary ground wheel unit includes a plurality of auxiliary ground wheels arranged transversely of the vehicle body. The plurality of auxiliary ground wheels arranged in the right and left direction increase the width of contact with the ground. This contributes to stable traveling of the vehicle by contacting the ground in a plurality of locations, and by preventing the auxiliary ground wheel unit from falling into hollows of the ground. As a result, with the auxiliary ground wheel unit having a stable contact with the ground, the orientation of the vehicle body is stabilized to improve grass cutting quality.
In another preferred embodiment of the invention, the support member includes a proximal arm portion extending longitudinally of the vehicle body and laterally outwardly of the engine and having a front end thereof connected to a body frame to be pivotable about an axis extending transversely of the vehicle body, and a distal arm portion extending transversely of the vehicle body from a rear end of the proximal arm portion, with an extended end having the auxiliary ground wheel unit attached thereto. With this construction, even when the mower draws too close to a tree or the like, the proximal arm portion extending laterally of the engine protects the engine from directly striking the tree or the like. In other words, the support member acts as a protector for the engine.
The proximal arm portion of the support member may be disposed laterally of the vehicle body opposite from a side where a blower is disposed for transmitting grass clippings into a grass catcher. Then, the proximal arm portion of the support member is allowed to move up and down through an increased range without interfering with the blower.
When the lawn mower engages in an operation, turning around a tree or the like, the side having a grass outlet of the mower unit lies outwardly of the turning circle. Where the proximal arm portion of the support member is disposed laterally of the vehicle body opposite from the side where the grass outlet of the mower unit is disposed, the support member lies inwardly of the turning circle. Thus, the support member acts as a protector to keep the engine out of direct contact with the tree or the like when the mower draws too close to the tree or the like.
In yet another preferred embodiment of the invention, the auxiliary ground wheel unit is disposed such that the auxiliary ground wheel unit describes a turning track within a maximum turning track of the lawn mower when the right and left rear wheels are driven at an equal speed in opposite directions to steer the vehicle body. If the auxiliary ground wheel described a maximum turning track of the mower when the vehicle body is steered by driving the right and left rear wheels at the same speed in opposite directions, the auxiliary ground wheel would be liable to strike an obstacle such as a tree or a wall as an operator operates and turns the mower around the obstacle while looking ahead. However, the aforesaid structure eliminates the possibility that the carelessness of the operator causes the auxiliary ground wheel to strike an obstacle. The operator has only to pay attention to the most forwardly projecting part of the mower.
Furthermore, from the viewpoint of the operator skill in driving the lawn mower, it will be convenient if the auxiliary ground wheel unit is disposed such that the auxiliary ground wheel unit describes a turning track not exceeding a turning radius of the right and left rear wheels when the right and left rear wheels are driven at an equal speed in opposite directions to steer the vehicle body. With this structure in which the auxiliary ground wheel unit turns with a radius not exceeding that of the right and left rear wheels, the auxiliary ground wheel will have no possibility of colliding with an obstacle as long as the operator turns the lawn mower near the obstacle with care so that the rear wheels move clear of the obstacle.
It will also be convenient if the auxiliary ground wheel unit is disposed such that the auxiliary ground wheel unit describes a turning track not exceeding a turning radius of the front wheels when the right and left rear wheels are driven at an equal speed in opposite directions to steer the vehicle body. With this structure in which the auxiliary ground wheel unit turns with a radius not exceeding that of the right and left front wheels, the auxiliary ground wheel will have no possibility of colliding with an obstacle as long as the operator turns the lawn mower near the obstacle with care so that the front wheels move clear of the obstacle.
Other features and advantages of this invention will be apparent from the following description of the embodiment to be taken with reference to the drawings.